A process and apparatus for microwave fusing are disclosed in U.S. 2003013034. Resonators that are arranged at right angles to the plane of the printed matter for fixing the toner are used, which overlap each other's effective widths in an appropriate set over the width of the printed matter. Accordingly, this width, which extends transversally to the transport direction of the printed matter, can be covered with the treatment fully without gaps. As shown more specifically in FIG. 3, the intensity of the electric field Ex, which is applied in parallel to the width direction of the printed matter, should be trapezoidal and almost rectangular. This can be seen in the resonator power distribution in the x direction.
It is possible in principle to find a resonator with a desirable or almost desirable power distribution profile. Regarding the trapezium profile, the side steepness of the actual field intensity distribution or power distribution for the real resonators depends on the required overlap of the adjacent resonators. The overlap area presents the risk that depending on the side steepness and overlap width, toner strips that are within the overlap area will be heated too much or too little. The ideal would be to have a precisely rectangular field profile, with an infinitely high-side steepness, so that no overlap is required. It is, however, very hard from the technical standpoint to implement this field profile. Further, inaccuracy of the printed matter transport also adds to the problem. If the transport and guidance direction of the printed matter is not exactly parallel with the longitudinal edge of the resonators, areas of the printed matter will not be heated, or they will be heated only a little when the overlap area is small. This may result in the problem of non-uniform heating and impairs the fixing results.
With inaccurate printed matter transport, the flatter sides can even be to advantage. The uniformity of heating over the width of the printed matter in this case will be better because of the gradual nature and overlapping of the effective area of a plurality of resonators working together, making the performance non-sensitive to the transport accuracy.
Further, a cooling device is located in the zone of the resonators, which cools down the printed matter in such a manner that the toner temperature is below its glass transition temperature. The cooling device can have an undesired effect on heating of the toner within the overlapping area of the resonators. If, for example, the cooling air is blown in the overlap area, and the printed matter in this area is cooled strongly, the fixing results in this area change. Also with regard to this, the overlap area can be of a profile insensitive to influence by shaping the side field intensity steepness of the resonators.
The disadvantage with the flatter side profile is that the overlap area should be made wider, with more resonators or wider resonators, (also referred to as applicators), in order to fix the toner over the entire width of the printed matter. It is, therefore, required in the state of the art that the profile of the resonator power profile be chosen in such a manner, for example, as to have the overlap as small as possible on the one hand, and on the other hand, to assure high process stability.